Optical measuring instruments usually require one or more light sources, which are expensive in terms of acquisition and/or the required installation space, such as is the case for lasers. To minimize cost, it is therefore desirable to use a light source in various instruments or at different inputs of a multi-function measuring instrument, so that a separate light source does not have to be provided for each measuring instrument or each input. The light source should be flexible in use and also be easy to combine with other light sources. In this way, each light source may be optimally exploited and utilized.
To this end, a modular apparatus for providing a laser beam is described in DE 103 61 177 A1 with defined interfaces to the outside. The apparatus may be sequentially connected to various measuring instruments. The manual changing of the connections (re-plugging) from one measuring instrument to another, however, is not easy to effect and is time consuming.
A greatly improved modular laser source is known from U.S. Pat. No. 7,760,776 B2. It may comprise an optical switch for switching between two or more optical outputs. This optical switch may, in particular, comprise a movable mirror. As a result of the ability to switch, several measuring instruments (or several inputs of the same measuring instrument) may remain permanently connected to the device. Time-consuming manual re-plugging is then no longer necessary. However, no automatic switching is described, so that switching is slow.
Modern microscopes allow the implementation of various methods on the same stand. One example is the combination of the techniques of fluorescence recovery after photo-bleaching (FRAP), total internal reflection (TIRF) and confocal scanning. A confocal scanning microscope may be either a point scanning system, such as a laser scanning microscope, or a multifocal scanning system, for example based on a Nipkow disk, as well as a line scanning system. Typically, in such combinations, the individual sub-processes are carried out repeatedly at specific time sequences of a few milliseconds during a measurement cycle. Manual changing of the input is thus avoided.
A further problem arises when the outputs of an optical switch are irradiated inaccurately (for example, the switchable beam falls partially or completely next to the chosen output—positioning error—or at an angle to it—angular error). This can lead to loss of intensity while, under certain circumstances, a part of the beam may not reach the output. This is especially true when the outputs are constructed as fiber couplers, as these are highly sensitive with respect to the incident angle and the incident position of the beam. Problematically, these errors may, in spite of an initial high-precision adjustment of the beam paths, occur only during a measurement, for example because of thermally-induced changes in the optical geometry of the laser, the beam paths to the switch and/or the switch itself. In addition to permanent intensity losses, undesirable fluctuations in intensity may then occur, particularly during a measurement. Such undesirable fluctuations may also occur during the actual switching operation due to the input and output processes of the switching mirror.
A detection-side optical switch with a galvanometer as a switching mirror is described in US 2011/0102887 A1. Switching is slow due to the inertia of the galvanometer mirrors. Due to the temperature sensitivity of galvanometer mirrors, the accuracy of the switching and the stabilization during the course of a measurement is not guaranteed. This also applies to environmental variations of the beam paths, such as temperature fluctuations.
The optical switch described in JP-A 2011158688 enables faster switching in the range of milliseconds. It comprises a matrix of micro-mirrors that is adjustable by means of an actuator in the form of a micro-electro-mechanical system (MEMS). This allows for the distribution of a light beam to a plurality of outputs having variable relative splitting ratios. The switching between the outputs is fast, but again becomes inaccurate during the course of a measurement. The actual switching process is slow until a defined mirror position is reached because of the input and output processes.
A more accurate method of controlling optical switches in telecommunications technology is known, for example, from WO 01/24384 A2 and is based on two series-connected micro-mirrors driven by a MEMS. In this case, control of the mirror positions is effected by means of a pilot light beam that is reflected into the light beam upstream of the foremost mirror, and is detected in a respective quadrant diode per switch output downstream of the rearmost or back mirror for use in the control of the mirror positions. However, this type of control requires relatively long switching times between the various outputs until a defined mirror position is reached because of the input and output processes. The inaccuracy in the presence of thermal changes in the environment is also still relatively large.